Ullnasjön — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Ullnasjön, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Ullnasjön today is 18.9°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
⚠️ As of today, the minimum water temperature ranges from 65°F (18°C) to 68°F (20°C). This is already quite warm water, which is ideal for most people. Swimming becomes comfortable, and prolonged stays in the water do not cause discomfort. This temperature is perfect for family trips and for those who prefer warmer water. It is also comfortable for water sports such as surfing or swimming. It is important to note that these swimming tips and recommendations apply only in good weather. When the air temperature is below 68°F (20°C), and sometimes even below 77°F (25°C), swimming can be unpleasant even with relatively high water temperatures.
Water Temperature Chart Over the Last 30 Days
Table of Daily Sea Temperature Data
| Date | Current | Average | Forecast |
|---|---|---|---|
| AUG 24 | 18.0°C | 22.0°C | |
| AUG 25 | 18.0°C | 22.0°C | |
| AUG 26 | 18.0°C | 22.0°C | |
| AUG 27 | 18.0°C | 22.0°C | |
| AUG 28 | 18.2°C | 22.0°C | |
| AUG 29 | 18.1°C | 22.0°C | |
| AUG 30 | 18.1°C | 22.0°C | |
| AUG 31 | 18.1°C | 22.0°C | |
| SEP 1 | 18.0°C | 18.9°C | |
| SEP 2 | 18.0°C | 18.8°C | |
| SEP 3 | 18.0°C | 18.8°C | |
| SEP 4 | 18.0°C | 18.7°C | |
| SEP 5 | 18.0°C | 18.7°C | |
| SEP 6 | 18.0°C | 18.6°C | |
| SEP 7 | 18.0°C | 18.6°C |
* Current - Actual water temperature value
** Average - Average water temperature on this day in recent years
*** Forecast - Our water temperature forecast
Actual nearshore water temperatures may fluctuate by several degrees from the reported values, especially following heavy rainfall or extended periods of strong winds. Certain wind patterns can cause colder, deeper waters to rise and replace the sun-warmed surface water, leading to noticeable variations.
Our forecast is based on a proprietary mathematical model that considers real-time water temperature changes, historical trends, key weather patterns, wind strength and direction, and air temperature specific to each region. Additionally, we incorporate data from other resorts to enhance accuracy.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Min | Avg | Max |
|---|---|---|---|
| January | 0°C | 3°C | 6°C |
| February | 0°C | 3°C | 6°C |
| March | 0°C | 4°C | 7°C |
| April | 3°C | 8°C | 11°C |
| May | 7°C | 12°C | 18°C |
| June | 12°C | 18°C | 24°C |
| July | 15°C | 21°C | 27°C |
| August | 17°C | 22°C | 27°C |
| September | 12°C | 18°C | 23°C |
| October | 7°C | 11°C | 14°C |
| November | 3°C | 7°C | 10°C |
| December | 0°C | 4°C | 7°C |
Ullnasjön: Water Temperature by Location
Ullnasjön: Weather Forecast
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Location & Local Information
Ullnasjön, a freshwater lake in Stockholm County, typically shows clear seasonal variation in water temperature. In winter the surface usually approaches freezing and may be ice-covered, with liquid water close to 0–4 °C (32–39 °F) beneath the ice. During spring the lake warms to roughly 2–10 °C (36–50 °F) as ice melts and runoff cools the water. By early to mid-summer temperatures commonly reach 12–18 °C (54–64 °F), with peak summer highs often in the 18–22 °C range (64–72 °F) and occasional warm spells pushing surface readings toward 24 °C (75 °F). In autumn the surface cools again, dropping from around 14–8 °C (57–46 °F) to single digits as the season progresses.
Swimming in Ullnasjön is generally allowed and practiced, especially in the warmer months, because Sweden’s right of public access (allemansrätten) permits entering natural shorelines while respecting private property. Municipal authorities may monitor water quality at popular bathing spots, so checking local advisories is wise. Safety considerations include cold-water shock at lower temperatures, underwater vegetation, boat traffic and variable depths; ice swimming does occur locally but requires careful assessment of ice thickness and safety measures. Recreational swimming is common in summer when temperatures are most comfortable, while winter activity is limited to supervised or experienced winter-bathing situations.